/*
 * Copyright (c) 2011-2012 Alexander Dubu
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * o  Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * o  Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * o  Neither the name Axil nor the names of its contributors may be used to
 *    endorse or promote products derived from this software without specific
 *    prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

package axil.stdlib.core.construct;

import axil.api.AxilObject;
import axil.api.extend.Environment;
import axil.api.extend.Parameters;
import axil.api.extend.Source;
import axil.compiler.api.Emitter;
import axil.compiler.api.ScopeInjector;
import axil.compiler.ast.Node;
import axil.stdlib.collection.type.Range;
import axil.vm.opcode.Opcode;
import axil.vm.stack.StackFrame;

import java.util.List;

import static axil.framework.Functions.replace;


/**
 * An expression where multiple values can be declared at once and placed into
 * the context for execution. For example:
 * <pre>
 * 		with(
 * 			val(a, expr),
 * 			val(b, expr),
 * 			body()
 * 		)
 * </pre>
 */
public class With extends Special implements ScopeInjector, Emitter {
	private int[] ids;
	private Val[] vals;
	private AxilObject body;


	/**
	 * This constructor is used only when creating anonymous instances suitable
	 * for loading the function definition. Use this with caution! This is not
	 * meant to create an executable object.
	 */
	public With() {
	}


	private With(Source source, Val[] vals, AxilObject body) {
		super(source);
		this.vals = vals;
		this.body = body;
		final int size = vals.length;
		this.ids = new int[size];
		for (int i = 0; i < size; i++) {
			ids[i] = vals[i].id();
		}
	}


	/**
	 * Tell if the variable identifiers are given directly in this function (as
	 * with "let" or "func") or are indirectly declared in a subsidiary function
	 * (as with "with").
	 */
	public boolean indirect() {
		return true;
	}


	/**
	 * Indicate any new identifiers defined by the given arguments. The range
	 * of values in which identifiers can be expected is returned. A null value
	 * is returned if the number of arguments given is not valid for this
	 * function.
	 */
	public Range injects(int args) {
		if (args < 2) {
			return null;
		}
		return new Range(0, args - 2);
	}


	/**
	 * Relink this instruction, replacing the bad variable ID with the good
	 * variable ID. This is used when linking code that contains forward
	 * references, allowing us to compile in a single pass, but correct later.
	 */
	public void relink(int bad, int good) {
		replace(ids, bad, good);
		for (Val v : vals) {
			v.relink(bad, good);
		}
		replace(body, bad, good);
	}


	/**
	 * Emit a new instance of this function using the indicated arguments. This
	 * method can safely assume that the number of arguments required are being
	 * provided.
	 */
	public Opcode emit(Source source, List<Node> args) {
		final int size = args.size() - 1;
		Val[] v = new Val[size];
		for (int i = 0; i < size; i ++) {
			v[i] = new Val(args.get(i));
		}
		return new With(source, v, args.get(size).emit());
	}


	/**
	 * Evaluate this object in the given context and environment. A non-null
	 * object must be returned.
	 */
	protected AxilObject evaluate(Environment env, Parameters params) {
		StackFrame sf = StackFrame.create(params, this, ids);
		final int size = vals.length;
		for (int i = 0; i < size; i++) {
			sf.at(i, vals[i].eval(env, params));
		}
		return body.eval(env, sf);
	}
}
